Measure your piston carefully. Measure at 90 degrees from the wrist pins and about 1/4" up from the bottom of the skirt. Measure your block at about 1/4 below the desk. Subtract the piston measurement from the block measurement and you have your piston clearance. Ideally you want between .0035 and .0055 clearance. If you have less, you will have to hone your bore out to get your ideal clearance.

***warning-this is best left to an experienced machine shop or kart shop.

  Kathy torques down the honing plate. The plate, which comes in the tool kit, produces the same streeses on the block as would the cylinder head.
  Using 200 and 500 grit stones, Kathy opens up the bore to the correct clearance. The YF200 uses a very high quality sleeve (from the drag racing world) and honing will require stones that are in excellent condition.
  A woman's work is never done. Kathy carefully cleaned the block in a hot water and Tide solution, rinsed it repeatedly and blew out all of the holes and cavities. You cannot be too clean at this point in the assembly.
  All of the messy stuff is now behind us and Kathy can start the fun part. She greases up the crankshaft and the main bearing and seals prior to installation.
  Slowly and carefully insert the crankshaft into the block.
  Lube the wrist pin and insert it into the connecting rod.
  Install the circlips, taking the usual caution to make sure the clip is seated completely in the land.
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